1. Field of the Invention
The present invention relates to a method of making a slider of a linear guide device for guiding a movable body such as a work table of a machine tool or an industrial robot or the like moving along a track rail arranged at a fixed portion such as a bed, a column or the like while applying a load on the track rail, particularly to a method of forming a slider by building up a synthetic resin onto a block main body made of a metal.
2. Description of the Related Art
There has been known a conventional linear guide device of such a kind constituted by a track rail that is arranged at a fixed portion such as a bed or the like and on which rolling faces of balls are formed and a slider integrated to the track rail via a number of balls for moving along the track rail while supporting a movable body such as a table or the like.
Further, the above-described slider is constituted by a movable block having load rolling faces opposed to the rolling faces of the track rail via balls and ball return holes in parallel to the load rolling faces, which is movable along the track rail by rolling the balls, a pair of end caps respectively fixed to forward and backward end faces of the moving block and having direction change paths of the balls for communicating and connecting the load rolling faces with the ball return holes and ball retainers attached to the moving block for preventing the balls from coming off from the load rolling faces when the slider is removed from the track rail. Also, end portions of the load rolling faces and the ball return holes are connected by the direction change paths by fixing the end caps to the forward and rearward end faces of the moving block whereby infinite circulation paths of balls are completed in the slider.
Meanwhile, according to the conventional slider for the linear guide device constituted as described above, boring of the ball return hole, attaching operation of the ball retainers and the like are needed with respect to the moving block and considerable time and labor is required in manufacturing the slider. Therefore, the applicants have proposed to manufacture the slider by utilizing an injection molding process of a synthetic resin (Japanese Unexamined Patent Publication No. JP-7-317762).
Specifically, a synthetic resin is built up by injection molding onto a block main body made of a metal where the above-described load rolling faces have been ground and the ball return holes and the ball retainers are integrally formed with the block main body in the injection molding by which the moving block is manufactured, which is provided with an advantage whereby a moving block having a complicated shape can easily be manufactured.
Meanwhile, in building up a synthetic resin onto the block main body made of a metal, the ball retaining portions are formed on the both sides of the load rolling faces of the block main body as described above, where it is necessary to expose the load rolling faces per se on which the balls run without putting the synthetic resin on the load rolling faces. Therefore, it is necessary to cover the load rolling faces against the molten synthetic resin in the injection molding.
Accordingly, conventionally, in fixing the block main body in the mold of the injection molding, a projected support portion provided on the side of the mold is brought into contact with the load rolling faces of the block main body and the load rolling faces are covered against the molten synthetic resin by the projected support portion.
However, when the load rolling faces are covered by bringing the projected support portion of the mold into direct contact with the load rolling faces, since the load rolling faces are formed in a curved face corresponding to the curvature of the ball, it is necessary to form the projected support portion in contact with the load rolling faces also in a curved face in compliance with the curvature of the load rolling faces and if the curved faces of both are not brought into accurate alignment, the molten synthetic resin forming the retainers invades a clearance therebetween.
Furthermore, when the molten synthetic resin invades the clearance between the load rolling faces and the projected support portion of the mold, the molten synthetic resin constitutes burrs of the synthetic resin covering the load rolling faces and the smooth running of the balls is significantly hampered under such a state. Also, once the ball retainers are formed on the both sides of the load rolling faces, the load rolling faces cannot be polished since the ball retainer becomes a hazard for the polishing operation and therefore, the constituted burrs cannot be removed. Accordingly, in the method of manufacturing the moving block utilizing the injection molding, a countermeasure for preventing the occurrence per se of burrs covering the load rolling face is indispensable.
Meanwhile, it is preferable to set the block main body to the mold with the load rolling faces which have been formed, as positioning references in fixing the block main body in injection molding, since the ball retaining portions are needed to form accurately in the positional relationship thereof with the load rolling faces.
However, it is difficult to position the block main body by bringing the load rolling faces in contact with the projected support portion on the side of the mold, which is also formed in a curved face since the load rolling faces are formed in a curved face as described above. Especially, when the load rolling faces face in different four directions, it is extremely difficult to accurately position the block main body in the mold.
Also, when the projected support portion of the mold is brought into contact with the load rolling faces, the load rolling faces, which have been ground in the finishing operation, may be damaged with high probability and the grinding operation of the block main body prior to the injection molding operation may be completely be ruined.